There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.
If this question can be reworded to fit the rules in the help center, please edit the question.

+1 because I've tried so many IDEs I don't even dare to remember..and NetBeans is the best, great balance between features and usability. If you just want an editor, then (G)Vim, but it has a learning curve (well worth it). Additionally, you can install jVi plugin for NetBeans and have the best of both worlds.
–
dr Hannibal LecterSep 19 '10 at 20:05

3

+1 because Netbeans has all the features you need for (PHP) programming: code completion, phpdoc, debugging, svn/git/cvs support, local history, etc. etc
–
eddy147Sep 23 '10 at 6:54

+1 for Netbeans because it supports debugging with XDebug, and useful features like "Go to defintion" or "Find usages", that you expect to find in a good Development IDE.
–
PisuOct 18 '11 at 20:06

This is an advanced editor/lightweight IDE with lots of features. Like Gedit, it has syntax highlighting for PHP and is extendible through plugins. It has some more advanced features than Gedit such as code folding. It can be installed from the repositories by installing the package geany and optionally geany-plugins.

I also use Geany for editing occasional PHP pages, but for main projects not comparable with Netbeans.
–
PisuOct 18 '11 at 20:07

I use Geany too for PHP Development. Scribble (note anything) and terminal (especially for accessing mysql from command line) are the most helpful feature that's provided.
–
metamorphNov 16 '12 at 15:20

When you double-click on a PHP variable in Geany, the dollar is not selected (BTW, the same holds for Bluefish). To me, this is a clear indicator that Geany (and Bluefish) cannot be taken seriously as a PHP editor.
–
Walter TrossDec 28 '12 at 18:55

Please split your answer up to one item a post so people can vote appropriately.
–
Marco Ceppi♦Sep 16 '10 at 20:20

2

Gedit+Plugins is an awesome editor for lots of things.
–
Oli♦Sep 16 '10 at 22:10

Gedit + plugins is the equivalent to what Notepad++ in Windows would be if it didn't have so much unnecessary featuritis cruft included in the default install. Just be sure to disable the "File Browser Pane" plugin. It is known to have a bug that causes gedit to take a lot longer to startup.
–
Evan PlaiceSep 17 '10 at 8:54

I use gedit for my PHP work - I don't think it needs something as heavyweight as Netbeans.
–
DilbertDaveSep 23 '10 at 18:01

How can i customize gedit to match the highlighting scheme in the screenshot?
–
NESJan 1 '11 at 16:23

You can use the same IDE on all systems and in addition to the simple features of a text editor you get all the additional stuff that you need for larger projects: context aware code completion, refactoring, integration of versioning systems, issue tracking, deployment to remote servers and much other stuff.

Komodo is (imho) better but is a bit too weight, expecially with big files that reference many other files (in your file include another one, Komodo scan it to get the function/classes it contains and offer them in the auto-completition function).